In U.S. Pat. No. 4,757,875, dated Jul. 19, 1988, owned by the same assignee as the instant application, a self propelled aerial work platform is disclosed wherein a pair of substantially parallel tubular arms are each pivotally connected at one end to the superstructure support frame, and at the opposite end to the riser frame assembly to which the telescopic boom assembly, having a work platform mounted on its outermost end, it pivotally connected.
The parallel tubular arms are typically rectangular in cross-section, having the same dimensions and spaced one above the other. While this parallelogram linkage has been satisfactory for its intended purpose, it has been found that heavier loads can be supported by the boom assembly if the lower arm, which is the tension member in the parallelogram linkage, is fabricated to have a larger cross-sectional configuration than the upper arm, which is the compression member in the parallelogram linkage. It has been further found that the compactness of the riser assembly is not sacrificed in using a larger lower arm by constructing the lower arm in such a manner that the upper arm of the parallelogram linkage nests within the lower arm in its fully lowered and fully raised positions.